This invention concerns partially fluorinated and fully fluorinated polymers that are substantially transparent to ultraviolet radiation at wavelengths from approximately 140 nanometer to 186 nanometers.
The semiconductor industry is the foundation of the trillion dollar electronics industry. The semiconductor industry continues to meet the demands of Moore""s law, whereby integrated circuit density doubles every 18 months, in large part because of continuous improvement of optical lithography""s ability to print smaller features on silicon. The circuit pattern is contained in the photomask, and an optical stepper is used to project this mask pattern into the photoresist layer on the silicon wafer. Current lithography is done using 248 nm light; lithography with 193 nm light is just entering early production. Alternate methods of lithography that do not use visible or ultraviolet light waves, i.e., the next generation lithographies utilizing X-rays, e-beams or EUY radiation have not matured sufficiently that they are ready to be adopted for production. The industry, through its international consortium SEMATECH, has concluded that 157 nm light based lithography will be the next technological step. 157 nm lies in the region of the spectrum referred to as the vacuum uv (VUV), which range extends from 186 nm down to below 50 nm. Use of this VUV lithography requires materials transparent in this range. Specifically, the new 157 nm optical lithography standard leads to a demand for new polymeric materials, based on the requirement for transparency at 157 nm. As use of this new technology develops, there remains a continuing need for improved materials useful at the shorter wavelengths.
Certain fluoropolymers have already been identified in the art as useful for optical applications such as light guides, anti-reflective coatings and layers, pellicles, and glues. Most of this work has been done at wavelengths above 200 nm where perfluoropolymer absorption is of little concern.
WO 9836324, Aug. 20, 1998, Mitsui Chemical Inc., discloses the use of resins consisting solely of C and F, optionally in combination with silicone polymers having siloxane backbones, as pellicle membranes having an absorbance/micrometer of 0.1 to 1.0 at UV wavelengths from 140 to 200 nm Data in the literature, together with applicant""s measurements, for fluoropolymers (see Table I below) demonstrate that, at least at 157 nm, C and F fluoropolymers have absorbances much larger than A/xcexc=0.1 to 1 as claimed by WO 9836324.
WO 9822851, May 28, 1998, Mitsui Chemicals, Inc., claims the use of photodegradation-resistant, tacky polymers that immobilize dust particles when coated on the inside of a pellicle frame. These tacky materials have compositions consisting largely of low molecular weight xe2x80x94(CF2xe2x80x94CXR) copolymers in which X is halogen and R is xe2x80x94Cl or xe2x80x94CF3. Higher molecular weight polymers such as poly(perfluorobutenyl vinyl ether), poly[(tetrafluoroethylene/(4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole)], poly(tetrafluoroethylene/hexafluoropropylene/vinylidene fluoride), poly(hexafluoropropylene/vinylidene fluoride), or poly(chlorotolylfluoroethylene/vinylidene fluoride) are added as a minor component to improve creep resistance. It should be noted that all exemplifications of this technology were with poly(chlorotrifluoroethylens) as the low molecular weight adhesive agent, that poly(chlorotrifluoroethylene) absorbs 157 nm light strongly, and that retention of tackiness after extended UV degradation (illustrated only at 248 nm), not transparency, was the only demonstrated advantage of the claimed formulations.
Japanese Patent 07295207, Nov. 10, 1995, Shinetsu Chem. Ind Co, claims double layer pellicles combining Cyto(trademark) CTXS (poly(CF2xe2x95x90CFOCF2CF2CFxe2x95x90CF2)) with Teflon(copyright) AF 1600 for greater strength. Both Teflon(copyright) AF 1600 and Cytop(trademark) absorb strongly at 157 nm (see Table 2).
U.S. Pat. No. 5,286,567, Feb. 15, 1994, Shin-Etsu Chemical Co., Ltd., claims the use of copolymers of tetrafluoroethylene and five membered cyclic perfluoroether monomers as pellicles once they have been made hydrophilic, and therefore antistatic, by plasma treatment. That the presence of five membered ring monomers and tetafuoroethylene is not sufficient criteria to yield A/xcexc less than 0.1, is illustrated in Table 2 where only one out of five such polymers meet this goal.
European Patent 416528, Mar. 13, 1991, DuPont, claims amorphous fluoropolymers having a refractive index of 1.24-1.41 as pellicles at wavelengths of 190-820 nm.
Japanese Patent 01241557, Bando Chemical Industries, Ltd., Sep. 26, 1989, claims pellicles usable at 280-360 nm using (co)polymers of vinylidene fluoride (VF2), tetrafluoroethylene/hexafluoropropylene (TFE/HFP), ethylene/tetrafluoroethylene (E/TFE), TFE/CF2xe2x95x90CFORf, TFE/HFP/CF2xe2x95x90CFORf, chlorotrifluoroethylene (CTFE), E/CTFE, CTFE/VF2 and vinyl fluoride (VF).
Japanese Patent 59048766, Mar. 21, 1984, Mitsui Toatsu Chemicals, Inc., claims the use of a stretched film of poly(vinylidene fluoride) as having good transparency from 200 to 400 nm.
Many of the fluoropolymers cited in the references above are noticeably hazy to the eye because of crystallinity and would therefore be expected to scatter light to a degree unsuitable for high light transission and the accurate reproduction of circuit patterns. Poly(vinylidene fluoride), poly(chlorotrifluoroethylene), poly(tetrafluoroethylene/ethylene), commercially available poly(tetrafluoroethylene/hexafuoropropylene) compositions, and poly(ethylene/chlorotrifluoroethylene) are all such crystalline, optically hazy materials. More recent references have thus been directed at Cytop(trademark) and Teflon(copyright) AF because they combine perfluorination with outstanding optical clarity, solubility, and a complete lack of crystallinity. As shown below in the Discussion, however, Cytop(trademark) and most grades of Teflon(copyright) AF do not have the required transparency at 157 nm.
It is an object of the present invention to overcome the difficulties associated with the prior art by providing partially fluorinated and fully fluorinated polymers that are substantially transparent to ultraviolet radiation at wavelengths between 140 and 186 nanometers, especially at 157 nm.
This invention provides a process or method comprising
causing electromagnetic radiation in the wavelength range of 140 to 186 nanometers to be emitted from a source thereof;
disposing in the path of at least a portion of the so emitted radiation a receptor responsive to electromagnetic radiation in the wavelength range of 140 to 186 nanometers so that a pattern in space or time is thereupon imposed;
disposing between said source and said receptor at least one optical element having an absorbance/micrometer of  less than 1 said optical element comprising
an amorphous polymer selected from the group consisting of a copolymer of CH2xe2x95x90CHCF3 and CF2xe2x95x90CF2, a copolymer of CH2xe2x95x90CFH and CF2xe2x95x90CFCl, a copolymer of CH2xe2x95x90CHF and CClHxe2x95x90CF2, wherein said copolymers the ratio of monomers ranges from approximately 1:2 to approximately 2:1; a copolymer comprising two or rare different monomer units represented by the formula CX2xe2x95x90CH2 where X is F or CF3; a copolymer of xe2x89xa660 mole % 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole and one or more monomer; represented by the formula CX2xe2x95x90CH2 where X is F or CF3; a copolymer of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and 4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole; a copolymer of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and vinylidene fluoride; perfluoro(2-methylene-4-methyl-1,3-dioxolane));
and,
extracting information from the pattern so imposed.
This invention also provides an optical system comprising
a source of electromagnetic radiation in the wavelength region of 140 to 186 nanometers,
a receptor disposed within the optical path of at least a portion of the radiation which may be emitted from said source said receptor having a sensitivity to radiation in the wavelength region of 140-186 nanometers,
at least one optical element disposed between said source and said receptor, said element having an absorbance per micrometer of  less than 1.0 in the wavelength region of 140-186 nanometers,
wherein said optical clement comprises an amorphous polymer selected from the group consisting of a copolymer of CH2xe2x95x90CHCF3 and CF2xe2x95x90CF2, a copolymer of CH2xe2x95x90CFH and CF2CFCl, a copolymer of CH2xe2x95x90CHF and CClHxe2x95x90CF2, wherein said copolymers the ratio of monomers ranges from approximately 1:2 to approximately 2:1; a copolymer comprising two or more different monomer units represented by the formula CX2xe2x95x90CH2 where X is F or CF3; a copolymer of xe2x89xa660 mole % perfluoro-2,2-dimethyl-1,3-dioxole and one or more monomers represented by the formula CX2xe2x95x90CH2 where X is F or CF3; a copolymer of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and perfluoro(2,2-dimethyl-1,3-dioxole); a copolymer of perfluoro(2-methylene-4-methyl-1,3-dioxolane) and vinylidene fluoride; poly(perfluoro(2-methylenemethyl-1,3-dioxolane)),
and,
a means for creating a pattern of the electromagnetic radiation emitted from said source when said radiation is incident upon said receptor.
This invention further provides pellicles, anti-reflective coatings, optically clear glues, light guides and resists comprising the UV transparent material provided above.
This invention further provides copolymer compositions comprising poly(hexafluoroisobutylene:triuoroethylene) with 40-60 mole % hexafluoroisobutylene and 60-40 mole % tifluoroethylene.